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Fair Value Measurements. (Details) - USD ($) | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Fair Value Measurements. (Details) [Line Items] |  |  |
Property and equipment held-for-sale at fair value | $ 48,548,000 | $ 70,400,000 |
Issued pre-funded warrants | $ 0.001 |  |
Exercise price | 9.76 | $ 1.00 |
Pre-funded Warrants and Other Warrants [Member] |  |  |
Fair Value Measurements. (Details) [Line Items] |  |  |
Exercise price | $ 9.757 |  |

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